Melanoma is the most aggressive type of skin cancer, and is the leading cause of death among skin diseases. According to the estimate of the National Cancer Institute of USA, in 2013, 76,690 Americans will be diagnosed with melanoma, while 9,480 people will die from this disease. About half of melanoma patients carry a mutated BRAF protein kinase gene. This abnormal mutation can promote the growth and spread of melanoma, and V600 accounts for the majority. Unfortunately, the chemotherapy using cytotoxin dacarbazine was the main treatment for malignant melanoma before 2011. Dacarbazine is a DNA alkylation drug that not only has a significant side effect, but also has a response rate of only about 10%, and the 1-year survival rate is only about 36%. In 2011, the launch of two breakthrough new drugs, Yervoy and Zelboraf, changed the status of melanoma treatment. On May 29, 2013, the USA Food and Drug Administration (FDA) approved a new drug Mekinist (trametinib) developed by GlaxoSmithKline (GSK) for the treatment of advanced or unresectable melanoma. Mekinist, as a single-drug oral tablet, is the first MEK inhibitor, and is suitable for the treatment of adult patients suffering from unresectable melanoma or metastatic melanoma carrying BRAF V600E or V600K mutation. The BRAF V600E mutation accounts for about 85% of all BRAF V600 mutations in metastatic melanoma, and the V600K mutation accounts for about 10% of all BRAF V600 mutations in metastatic melanoma. In a Mekinist trial of 322 patients, the survival was extended by 3.3 months in patients receiving Mekinist treatment compared with patients receiving chemotherapy.
CN103998041A discloses an oral solid formulation of the MEK inhibitor trametinib. The excipients used in this solid formulation are substantially free of water, so as to solve the problems of the stability, the dissolution rate of the solid formulation, and the adverse pharmacodynamics caused by the desolvation of the trametinib solvate when administered in vivo.
CN104902876A discloses a powder formulation comprising trametinib and a solubilizing agent, and the solubilizing agent is selected from cyclodextrin-based pharmaceutical auxiliary materials, so as to solve the problems of the dissolution rate of the powder formulation and the desolvation of the trametinib solvate when administered in vivo.
WO2015058589 discloses and is directed to 2-((2-fluoro-4-iodophenyl)amino)-1-methyl-4-((6-methylpyridin-3-yl)oxy)-6-oxo-1,6-di hydropyridine-3-carboxamide or a pharmaceutically acceptable salt thereof, which is useful as an inhibitor of MEK activity, especially in the treatment of cancer. WO2016155473 discloses the crystal form I of 2-((2-fluoro-4-iodophenyl)amino)-1-methyl-4-((6-methylpyridin-3-yl)oxy)-6-oxo-1,6-di hydropyridine-3-carboxamide p-toluenesulfonate (compound A) and a method for preparing the same.

Forms of a pharmaceutically active compound having low solubility may encounter a number of challenges in the preparation of a high quality solid pharmaceutical composition or solid formulation (such as tablets, granules, and micro-powder). The solubility of compound A and its salts is low, and none of the above documents mentions how to solve such problems so as to provide a composition having a satisfactory dissolution rate.